Transmitter for coded carrier control systems



A. FINLAY March 16, 1953 TRANSMITTER FOR CODED CARRIER CONTROLl SYSTEMS Filed June 26, 1951 JNVENToR. A lexandel Finlay HIS ATTURNY Patented Mar. 10, 1953 l.

TRANSMITTER FOR CODED CARRIER CONTROL SYSTEMS Alexander Finlay, Swissvale, Pa., as signor to Westinghouse Air Brake Company, Wilmerdmg, Pa., a corporation of Pennsylvania Application June 26, 1951, Serial No. 233,626

3 Claims.

My invention relates to transmitters for coded carrier control systems.

In many control systems it is desirable to use a single transmitting circuit or medium for the transmission of a plurality of different control signals. Furthermore, these control signals are often selectively directed to different locations spaced along the transmitting circuit with each location requiring a plurality of different controls. It has been proposed to use in such a control system a plurality of different carrier currents with each current providing a signaling channel and over each channel of which a plurality of different signals are transmitted by coding the carrier. In these control systems it is desirable that'the -channels be closely spaced as to the carrier frequency in order to conne the entire system to a relatively narrow band of carrier frequencies.

Also, in these control systems the different controls for each channel are frequently provided by the corresponding carrier being interrupted according to a designated code, the code consisting of spaced pulses of the carrier current. That is to say, the carrier is coded by. interrupting the carrier at a designated code pattern. In other words, these contro1 systems may be of the time code type.l

When a control signal is provided by interrupting a carrier, the control signal supplied to the transmitting circuit has a Wave form which corresponds to the carrier frequency amplitude modulated by the code frequency. This causes the energy supplied to the transmitting circuit or medium to lcontain the fundamental frequency of the carrier and side-band frequency components which are equal to the carrier frequency plus or minus n' times the coding frequency where n is any integer.

These side-bands, and especially the higher order of the side-band components, may cause serious adjacent channel interference where closely spaced channels and acommon transmitting medium are used.

Accordingly, it is an object of my invention to provide. an improved transmitter for a coded carrier control system where the carrier is coded by being interrupted according to a code pattern.

. Another object of my invention is the provision of a coded carrier transmitter incorporating novel means for shaping the wave form of the coded energy supplied by the transmitter.

A further object of my invention is the provision of improved means for keeping the oscillator of a Icode transmitter to produce a square Other objects, features and advantages of myv invention will appear as the specicationprogresses. .f To accomplish the foregoing objects, features and advantages of my invention I provide ka vacuum tube oscillator which is keyed by coding means interposed in the anode circuitof the oscillator tube and whichcoding means is operaf tive to interrupt the anode power supply in ac: cordance with any one of a plurality of different code patterns. Thus the output of the oscillator has a wave form which is the carrieramplitude modulated by a square top wave. Preferably, I provide a buffer amplifier the input electrodes of which are coupled to the oscillator through 'a unit interposed in the cathode circuit of the os-fr 4cillator tube. Furthermore, the buffer amplifier stage is arranged preferably as a grounded grid amplifier. I also provide an interstage coupling` unit and a power amplifier the inputV electrodes of which are coupled to the buffer amplifier out-y put electrodes through the couplingrunit. interstage coupling unit is constructed .andprol portioned to remove all.sidefbandcomponents that are unwanted in the coded signal energy supplied .by the transmitter to thetransmitting medium. That is to say, this coupling unit characterized to pass a selected band of the side-L.-

band frequency components along with the car#V rier frequency and the remaining side-band com.- ponents are suppressed. The band of side-band frequency .components passed is selected so that.

a satisfactory code signal is provided. The loutput of the terminals of this coupling unit are'v connected to the input electrodes of the power amplifier and the output electrodes of the poweramplier are in turn coupled to the transmitting circuit.

"In this way there is supplied to the transmitting circuit code pulses of the carrier and vwhich pulses contain the fundamental frequency of the carstantially suppressed.

I shall describe a preferred form of a'coded carrier transmitter embodying my invention .and

shall then point out'the novel features thereof' in claims.

A The accompanying drawing is a schematic dia-' gram showing a preferred construction of a coded carrier transmitter embodying my invention when used with a time ycode type of control system.

Referring to the drawing, the reference characters LI and L2 designate a pair of line wires extending between an ofce OF and a plurality of spaced field stations of which only the one eld station FS is illustrated because this one station is suicient for an understanding of my invention. These line wires LI and L2 provide a transmitting circuit between the -oliice and the field stations and by which circuit diiferentrcode control signals are transmitted. from the oice to the different stations. It is to be understood that while the transmitting circuit or .medium is here illustrated as comprising a physical pair of wires, the transmitting medium may take other forms and it may be a radio link extending between the oflice and theleld stations. Furthermore, it is clear that this transmitting circuit is capable of being used as a common medium for the transmitting of a plurality of carriers of different frequencies with each carrier providing an. individual signaling channel and each of which channels is capable of providing a plurality of different code signals by code interrupting the carrier of the corresponding channel. The oi'ce OF is provided 'that a plurality of transmitters, one for each signaling channel of the. system. As illustrated in the drawing, two transmitters A and B are provided, these transmitters being constructed according to my invention. Only the structure of the transmitter A is illustrated in the drawing, the transmitter B being shown in a conventional manner because its construction would be a duplication of that of Vtransmitter A except for the tuning of the different parts. By way of illustration, I shall assume vthat the transmitter A supplies a carrier of the frequency f I and the transmitter B supplies a carrier of the frequency f2. The outputs of these two transmitters A andB are connected to the transmitting circuit in multiple. The output of 'the ltransmitter A includes a transformer T'I, a secondary winding Ill of which is connected across the line wires L`I and L2 through a series tuned filter, an inductor 60 and a capacitor 62 in vseries being interposed in the lead from the secondary winding I!! to theline wires L2, and an inductor B1 and a capacitor '63 in series being interposed in the lead from the secondary winding vIll'to the line wire LI. Similarly, the trans# former T2 of the transmitter B is connected across the line wires LI and `L2 through a filter including inductance and capacitance. By this ter'v includes a twin triode vacuum tube VI, the' left-hand section of which as viewed in the drawingl is used as the electron tube of van oscillator and the right-hand section of which tube VI is used as a buffer amplifier stage. It isto'be'understood vthat other types of electron tubes can be used.. Specifically, the left-hand section 'of tubev VI .is Aprovided with an fanode I2, a cathode I3, and a control grid or electrode I4, and the -righthaIIdf-.fsection .ofl the-tube isprovided fwith/ an anode I5, a cathode IB and a control electrode I1.

The oflice OF is provided with a suitable power source for supplying power to the different tubes of the transmitter. As here shown, a high voltage direct current source is identified by the terminals B-land B-, the terminal B being connected to ground in the manner customarily employed in transmitters of this type. A low voltage source is also provided for heating the different tubes but this low voltage source and the associated heating circuits are not shown in the drawing in order to simplify the drawing ybecause these circuits would be in accordance with standard practice and they form no part of my present invention` The oscillator section of the tube VI is provided with a tuned oscillatory circuit comprising an inductor winding I8 and a capacitor I9, these two elements being tuned toresonance at the carrier frequency of the transmitter, and which I have here assumed as being a carrier-frequency fl. This oscillator tube is provided with an anode circuit that can be traced from terminal B+of the power source througha normally open con` tact 20 of a coding unit CU to be referred t'o shortly, wire 2 I, anode I 2 and tube space to'cathode I3, wire 22 to a selected intermediate terminal of the inductor winding I8, the vlowerporY tion of winding I8 and wire 23 to therterminal 13'- of the power source. The oscillator tube is also provided with a control circuit extendingrfrom the control electrode Id through a unit comprising a resistor 24 and avcapacitor =25 inmultiple; the upper portion of the inductor winding I8 to its intermediate terminal and wire 22V to the cathode I3. It is clear that vwhenthecontact 2l]A of the coding unit CU is closed and therpower source is connected across the anode vI2 'and the cathode I3 of the oscillator tube,theroscillator"is energized and its carrier frequency fl is generated. In other words, the oscillator is keyedby the coding unit CU which is operable to close its contact 28 at selected intervals, the carrier being supplied when the contact 20 is closed andl the carrier being interrupted when the contact 20 is open. It follows that code pulses of the carrier energy are supplied bythe :oscillator in vac` cordance with the code operation of the contact 20 by the coding unit CU.

The coding unit CU may .be of different forms' and as here shown it is a direct current polar relay type having its contact '20 kspring biased to an open position 'and operated to a closed \po"v is clear from vthe foregoing 'thatthe'coding Aunitl and the oscillator are operable to supply coded carrier vwhich corresponds to the carrier 'amplitude modulated according to the code frequency of the coding contact 20. Consequently, the en ergy output of the oscillatorwill have a wave form that comprises the fundamental frequency of the oscillator and side-'band frequency components which have a frequency corresponding to the carrier frequency plus or'minus'n times' the coding frequency where n is any integer;

The buffer amplifier, that is; the right-banal section of the tube -V I is arrangedasia grounded'- grid amplier which is coupledto the oscillator tube through the cathode circuit of the amplier. Specifically, the grid I1 of the buffer amplier is connected to ground by wire 29 and its cathode i6 is connected to the cathode I3 of the oscillator tube through a unit consisting of a resistor 21 and a capacitor 28 in multiple. The anode i of the buffer amplier is connected to the positive terminal B+ of the power source through input terminals of an interstage coupling unit ICU to be described shortly. Thus, the code pulses of the carrier resulting from operation of the coding unit CU will be reproduced in the anode circuit of the buffer amplifier at an energy level increased by the amplification of the buffer amplifier tube. It is clear, however, that the coded energy in the output of the buier tube will have a wave form that corresponds to the wave form of the energy supplied by the oscillator.

The interstage coupling ICU includes a pair of symmetrical tuned circuits. Speciically, a first tuned circuit includes an iron core inductor winding 36 and a capacitor 3l connected in multiple across the input terminals 32 and 33 of the unit, and to which input terminals the anode circuit of the buffer stage amplier is connected as explained hereinbefore. A second tuned circuit of the unit ICU comprises an iron core inductor winding 34 and a capacitor 35 connected in multiple to output terminals 36 and 31 of the unit, and across which output terminals a load resistor 38 is connected. The tuned circuits of the unit ICU are coupled by a capacitor 39, there being, however, a certain amount of inductive coupling between the two windings 30 and 34. It is to be pointed out that these two tuned circuits can be disposed for inductive coupling only or for capacitive coupling only or for both inductive and capacitive coupling.

The parts of the coupling unit ICU are constructed and proportioned for the unit to have a relatively flat band pass characteristic which is wide enough to permit a-steep rise in carrier voltage. Also, the unit is characterized so that a high attenuation is provided for frequencies outside of a selected band to suppress these nonselected frequency components of the energy. Preferably, the unit is characterized to` suppress the higher order of the side-band frequency components of the coded carrier energy. That is to say, the unit ICU is constructed andv characterized to pass the fundamental frequency of the carrier and a selected band of the sideband frequency components and to suppress the side-band frequency components outside of the selected band.

y Itis to be pointed out that this interstage coupling unit ICU could take other forms, but the construction here shown is the preferred arrangement. My invention, however, contemplates this unit to be constructed in any acceptable manner that will provide the above operating characteristics.

A power amplier PA is provided for amplifying the energy passed by the unit ICU and to supply the energy to the transmitting circuit Ll--L2. As here illustrated the power amplier PA includes a pentode V2 having an anode 40, a cathode 4I, a control grid 42 and two additional grids 43 and 44, the grid 44 being connected to the cathode 4l inside the tube. It will be understood, however, that other forms of tubes can be used. The tube V2 is provided with an input circuit by connecting its control grid 42 to a selected intermediate terminal of the load resistance 38 of the coupling unit ICU and connecting the cathode 4I to ground through a biasing unit consisting of a resistor 45 and a capacitor 46 in multiple, it being observed that the lower terminal of the load resistor 38 is connected to ground. The output or anode circuit for the power tube V2 extends from the power terminal B+ through wire 41, primary winding 48 of the transformer TI, anode 40 and tube space to cathode 4l and the biasing unit` 45--46 to ground. The grid 43 is preferably connected toA the positive terminal of the lpower source. As explained hereinbefore, the secondary Winding I0 of the transformer TI is connected to the transmitting circuit and consequently the coded carrier energy passed by the unit ICU is applied to the power amplifier PA and thence supplied to the transmitting circuit at a relatively high energy level, the wave form of the coded current supplied to the transmitting circuit corresponding to that passed to the output of the unit ICU.

The field station FS shown at the right-hand end ofthe drawing, is provided with receiving apparatus that includes a filter FI, amplifier decoding means AM, and a code following relay'64, and which receiving means is connected across the line circuit through leadv wires 65 and '66. This receiving apparatus for the field station FS may take diierent forms and it is shown in a conventional manner only because its specific form is no part of my present invention and it may be any one of several arrangements wellknown in the art. It is suiiicient for'this application to point out that this receiving apparatus is made selectively responsive to'the carrier pro-'- vided by the transmitter A and when coded carrier current is applied at the oihce OF by the transmitter A in the manner described hereinbefore, this coded energy is received at the station FS and decoded and the code following relay 64 is made to operate its contact 61 in step with the code operation of the contact 20 of the coding unit CU at the office. y y

A coded carrier transmitter here provided has the advantages that code distortion caused by the transmitter itself ,is largely eliminated. The transmitter can be used for systems having a high code speed and also for systems using a low code speed. The codeqpulses are shaped so as to minimize adjacent Vchannel `interference andyet pass a band of frequencies suihcient to assure reliable-reception at theY receiving station'. lFur-fthermore, the construction ofthe code transmitter here provided is relatively simple and inexpensive. x .L

Although I have herein shown and described but one form of transmitter for coded carrier control systems embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope oi' the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. A coded carrier transmitter comprising in combination, an oscillator including a tuned circuit and an electron tube having an anode, a cathode and a control electrode; said oscillator operable to supply a carrier of a selected frequency when power is applied across the anode and cathode of its tube, coding means having a contact which is operable to an open and a closed position at selected code rates, a power source, said power source being connected across the coded -carrier fhaving a :wave form "which lincludes said 'carrier frequency: and* side-band Ifrequency components of the l'carrier amplitude modulated atsa-i'dicode ratefrequency, a buer amplifier tuberfhaving input Aand output electrodes, means forr electrically couplingsaid bu'ier tubel input electrodes to -the :anode-cathode circuit of said oscillator tube, a coupling unitincluding .a .pair of*tunedslcircuitsand having input and output terminalspsaid ftuned :circuits of said unit Abeing electrically' cou-pled:andconstructed to pass only said-'carrier frequency andra selectedband of said side-band :components Yof 4the coded carrier, .said tuned circuits being;eiectivetorsuppress the sideband'rcomponents outside ofsaid selected band, saidfbuier amplifier havingr its outputelectrodes connectedto..-said= input terminals of the coupling ;.unit,la powerV amplifier tube having -input and output electrodes and having its inputelectrodes coupled to the output terminals of said unit,--and sending circuit means connected to the output :electrodes of saidpower amplifier tube.

2.'.A coded carrier transmitter comprising in combination, an oscillator including a tuned circuit yand Lan Aelectron tube vhaving an anode, a cathodeanda control electrode; said oscillator operable to supply a carrier of a selected frequency when `,power is lapplied-across the anode and cathode-ofy its-tube, coding means having a contact which is operable to an open and a closed position at '-selected kcode rates, a .power source, an. anode circuit including said contact and said power source connected across the anode and cathode of said oscillator tube, said oscillator being effective when thus energized to supply said carrier coded at the selected code rate of operationo'f said contact, said coded carrier having a wave form containing the fundamental carrier frequencyv and side-band frequency components equal tothe carrier frequency plus or minus 7L times the coding frequency wheren is 'any integer, a bufferamplifler tube having input and output electrodes, said buffer tube input electrodes being .electrically coupled to the cathode of said oscillatortube, a coupling unit including electrically coupledtuned circuitsand having input and .output terminals, said buffer tube output electrodes Vbei'n, .=rconnected to saidinput terminalsnfV said unitsaid tuned circuitshavinga construction `to characterize the unit to substantially suppress the higher .side-band frequency components of the coded vcarrier and tov pass the fundamental carrier frequency and selected lower side-band components, apowerramplier tube having input and .output electrodes, vcircuit means to electrically coupl `the output-terminalsfpf Vsaid unit to said.

input electrodes of saidfpower-'amplifier tube, another pair -of Loutput terminals, and means Ato electrical-lycouple saidzoutput electrodes ofrsaid power amplier tube `tosaid another pair of -output terminals. I

, 3.- In combinatioman oscillator including an oscillator-y circuit and .anelectron tube having an anode, -a cathode -and a control electrode; said oscillator operable to supply. a carrier of a selected vfrequency when energizecha ypower sourceeiiective to renergize'the oscillator, ya codingcontactoperable-to an-open and a closed `position at a selected-code rate, an anode-cathode circuit including said-,power source and -saidcontact connected to said anodeandcathode of said oscillator tube to energize-said Aoscillator at -said code rate to supply pulses of `said carrier, -said carrier pulses containing the `fundamental -carrier frequency and side-band lfrequency components due to theamplitude Vmodulation of the carriervby said codefrequencm a .buier amplifier tube` havinginput and loutput electrodes, means :including a coupling element to connect the 'input @electrode .of :the buffer -iamplier `to the cathode of said oscillator tube, a coupling unit including two, .symmetrically tuned circuits, each said .tuned circuit including inductance 1 and capacitance, said tuned. circuits 'being coupled 'by a-capacitor-connected to each of the circuits,l said coupling unit `characterized Vby suppressing a selected 'band of said side-band. components and passingV` the carrier and thenonselected sidebandcomponents'said unit having -input and output terminals,r` said output electrodes of -said` ALEXANDER REFERENCES CITEDy Y A The -followingreferences are offrecord :in the file of this patent:

UNITED-STATES vP-AIEN'IS mau`V y Name Y Date 11,836,441 Burkh'older Dec.. 15', A1931 2,229,029v Wass'ell June AZI, y1941 FOREIGN 'PATENTS Number Country Date 404382 Great Britain Jan.'18. 1934 

